Pick up any CCNA Exam Preparation Guide. There are plenty enough books or chapters and webpages dedicated to the topic of OSI Layer Model of Internetworking. I'm just providing a short summary of notes to remember. It's guaranteed that there will be questions of the 7 Layer OSI model, the Cisco three layer, model, and even the DoD's model and how all the layers interrelate.
Physical Topology - Defines how the computer and networking devices are connected (physical)
Logical Topology - Describes the path the signals travel from one path to another (routing, tunnels: layer 2 for ipsec, layer 4 for ssl)
ESSENTIAL FACTS
* Each layer of the OSI model is only interested in communicating with its peer later at the destination.
* Each layer provides services to the layer above it.
* Encapsulation: as application data parses down the protocol stack to transmit across network media, each layer adds a header or trailer (containing addressing information).
* OSI model uses structure, forms a good reference model, permits change at one layer without affecting the other layers
Cisco Hierarchical Three Layer Model
Access - provides work group access for end users, desktop layer
Distribution - routing protocols and security, includes LAN based routers and layer 3 switches, enables routing between VLANs
Core - high speed and redundancy, provides high speed data transfer between sites
TCP/IP Stack - 4 Layers
Application - Application, Presentation, Session
Transport - Transport
Internet - Network
Network Access - Data Link, Physical
CCNA Illustrated OSI Layer Graphics
OSI Model - 7 Layers
* Including some quick notes on the pdu, addressing used
Application - data
Presentation - data
Session - data
Transport - segment, port number
Network - packet, ip address
Data-Link - frame, mac address
Physical - bits
Application Issues: Application, Presentation, Session
Data Transport, Implementation details: Transport, Network, Data-Link, Physical
Therefore, the de-encapsulation first occurs at the Transport leve.
Application Layer
* Authentication
* Examples: email, file transfer, terminal emulation
Presentation Layer
* Data representation, such as the format or structure of data (say jpeg, wav etc)
* Negotiates data transfer, syntax
* Provides encryption
* http, ssh operates at this layer
* It's safe to say, it makes sure that information sent at the application layer of one system is readable by the application layer of the other.
Session Layer
* Client - server connection
* Inter host communication
* Establish, manage, terminate sessions between applications. Such as the Shopping Cart?
* Web server, data exchange
* Examples: NFS, SQL, Netbios
Transport Layer
* Establishes end to end connections between hosts
* TCP and UDP ports
* The source port in the UDP Header and TCP Header is a 16 bit calling port.
* Reliability and flow control (windowing)
* Establish, maintain, terminates virtual circuits
Network Layer
* Primarily deals with data delivery
* Routes data packets
* Selects the best path to deliver data
* Provides local addressing and path selection
* Manages connectivity
* IP addresses to route packets
The Ethernet source and destination address is a 6-byte hex
Data Link Layer
* MAC address
* Error detection
* Does Encapsulation Frame Relay or PPP ring a bell?
* The most diverse
Physical Layer
* Examples: Copper, wireless, satellite, fiber
* 1, 0 bits transmitted by electrical pulse, electrons, light
* Think Cabling
CCNA Illustrated OSI Layer Model Graphics Blog
Tuesday, February 14, 2012
Video Games in Military Training
I really should be studying for the CCNA Exam or building my test network to complete some router configurations. Perhaps I could find a good router simulation software, though nothing beats having to set up all the wiring and cabling by hand. Nonetheless, are there software packages for soldiers to do military training in a simulated environment, such as video games?
I stumbled upon an article debating whether a gamers make good soldiers. I've seen world class flight simulator programs made by the Canadian firm CAE. Reading on, I also discovered the Army's Engagement Skills Trainer (EST) to simulate the sound and feel of the different firearms used on the job for target practise. Well what happened to the firing ranges? I guess this makes an environmentally sound alternative without spent casings to clean up. The EST also provides possible scenarios to help soldiers make life changing decisions on when to shoot and when not to shoot. There was another simulator software called the Virtual Convoy Operations Trainer (VCOT) and DARWARS Ambush seems to be a big hit. DARWARS allows users to add or modify scenarios with their own learned experience.
Here's the link because it was such a page turner: http://science.howstuffworks.com/gamer-soldier2.htm
Now goes the question, if I played my daily dose of Wii golf, would that train me to be a world class golfer. Well I'd really have to say no because you need to feel the true weight of an expensive golf club, you'd have to feel the action and reaction of hitting a real ball, and experience real wind and air flow to influence the true path of the ball. There's no way to get that from a game.
In the same way, just studying for this exam on paper won't do. We don't want a CCNA "paper cert". Time to solve some real world router problems!
 |
| Source: Friend's Facebook post |
I stumbled upon an article debating whether a gamers make good soldiers. I've seen world class flight simulator programs made by the Canadian firm CAE. Reading on, I also discovered the Army's Engagement Skills Trainer (EST) to simulate the sound and feel of the different firearms used on the job for target practise. Well what happened to the firing ranges? I guess this makes an environmentally sound alternative without spent casings to clean up. The EST also provides possible scenarios to help soldiers make life changing decisions on when to shoot and when not to shoot. There was another simulator software called the Virtual Convoy Operations Trainer (VCOT) and DARWARS Ambush seems to be a big hit. DARWARS allows users to add or modify scenarios with their own learned experience.
Here's the link because it was such a page turner: http://science.howstuffworks.com/gamer-soldier2.htm
Now goes the question, if I played my daily dose of Wii golf, would that train me to be a world class golfer. Well I'd really have to say no because you need to feel the true weight of an expensive golf club, you'd have to feel the action and reaction of hitting a real ball, and experience real wind and air flow to influence the true path of the ball. There's no way to get that from a game.
In the same way, just studying for this exam on paper won't do. We don't want a CCNA "paper cert". Time to solve some real world router problems!
Monday, February 13, 2012
Cisco ICND1 Flashcard: IP Subnetting Quick Tips
Classes of IP Addresses
Sample Quiz
Will these IP's require a router to talk to each other? This is another way of asking are these hosts on the same network or subnet?
Given 192.168.1.0/ 24
Host a: 192.168.1.33/ 27
Host b: 192.168.1.50/ 28
Host c: 192.168.1.100/ 26
Host d: 192.168.1.90/ 27
There are whole chapters in books dedicated to subnetting. This can be easily simplified into two rows of numbers; it would be a very short book if I was writing it. This is like subnetting in your brain!
Write this down:
128 64 32 16 8 4 2 1
128 192 224 240 248 252 254 255
Start with Host a 192.168.1.33
/ 27 mask means a mask of 255.255.255.224
Then valid networks are 0, 32, 64, etc *
Network address would be .32
Valid hosts would be .33 to 62
Broadcast address would be .63
The number of subnets 2^3 = 8 where 3 is the number of masked bits or 1s
The number of hosts in each subnet 2^5 -2 = 30
* Finding the subnet base number
256 - mask = base number
Host b 192.168.1.50
/28 means a mask of 255.255.255.240
The valid networks would be 0, 16, 32, 48, 64 etc
Network address would be .48
Valid hosts would be .49 to 62
Broadcast address would be .63
Host c 192.168.1.100
/26 means a mask of 255.255.255.192
The valid networks are 0, 64, 128 etc
Network address is .64
Valid hosts .65 to 126
Broadcast .127
Host d 192.168.1.90
/27 mask means 255.255.255.224
Valid networks 0, 32, 64, 96
Network address is .64
Valid hosts .65 to .94
Broadcast .95
Answer, no body can talk to each other because they're on different subnets (different network addresses). A router would be required.
Binary Quiz
Convert 452 into binary
answer: 111000100
What is 11000111?
answer: 199
Convert 11101000111 into decimal
answer: 1863
A Class A network has 3 octets for the host field.
What is the practical minimum number of bits to borrow? 2
Using six subnet bits, how many usual subnets are created?
62
How many subnet bits do you borrow?
To see how many bits you should borrow from the host portion of the network address to give the required number of subnets, you should...
answer: substract the number of subnets you need from the network portion
Sample Quiz
Will these IP's require a router to talk to each other? This is another way of asking are these hosts on the same network or subnet?
Given 192.168.1.0/ 24
Host a: 192.168.1.33/ 27
Host b: 192.168.1.50/ 28
Host c: 192.168.1.100/ 26
Host d: 192.168.1.90/ 27
There are whole chapters in books dedicated to subnetting. This can be easily simplified into two rows of numbers; it would be a very short book if I was writing it. This is like subnetting in your brain!
Write this down:
128 64 32 16 8 4 2 1
128 192 224 240 248 252 254 255
Start with Host a 192.168.1.33
/ 27 mask means a mask of 255.255.255.224
Then valid networks are 0, 32, 64, etc *
Network address would be .32
Valid hosts would be .33 to 62
Broadcast address would be .63
The number of subnets 2^3 = 8 where 3 is the number of masked bits or 1s
The number of hosts in each subnet 2^5 -2 = 30
* Finding the subnet base number
256 - mask = base number
Host b 192.168.1.50
/28 means a mask of 255.255.255.240
The valid networks would be 0, 16, 32, 48, 64 etc
Network address would be .48
Valid hosts would be .49 to 62
Broadcast address would be .63
Host c 192.168.1.100
/26 means a mask of 255.255.255.192
The valid networks are 0, 64, 128 etc
Network address is .64
Valid hosts .65 to 126
Broadcast .127
Host d 192.168.1.90
/27 mask means 255.255.255.224
Valid networks 0, 32, 64, 96
Network address is .64
Valid hosts .65 to .94
Broadcast .95
Answer, no body can talk to each other because they're on different subnets (different network addresses). A router would be required.
Binary Quiz
Convert 452 into binary
answer: 111000100
What is 11000111?
answer: 199
Convert 11101000111 into decimal
answer: 1863
A Class A network has 3 octets for the host field.
What is the practical minimum number of bits to borrow? 2
Using six subnet bits, how many usual subnets are created?
62
How many subnet bits do you borrow?
To see how many bits you should borrow from the host portion of the network address to give the required number of subnets, you should...
answer: substract the number of subnets you need from the network portion
Friday, February 10, 2012
Canadian Navy invades Video game space
I always like it when the PM refers to Canadians coast to coast to coast. It reasserts Canada's sovereignty and three ocean boundaries. I also like how board games sometimes turn Geo-political too. I remember playing a good game of Mission Risk and Risk 2210 and the countries and nations we see today have boundaries barely recognizable, including Quebec as it's own sovereign entity. The moon is up for grabs and there are water colonies. Then there was the fiasco of Parker Brothers Monopoly Metropolitan Cities edition where coveted properties are labelled by city name and country. That was the case until the name Jerusalem, Israel became a hot issue and the game reverted to city names only. I believe Montreal and Toronto made the list! What is the capital of Canada again?
A Norway based game developer has launched a new video game set in 2030 when NATO and Russian forces go head to head for Arctic Sovereignty. Doesn't sound that futuristic to me. Especially the best ship Canada has to offer is the HMCS Halifax class frigate built in the 80's. Seriously? They couldn't come up with a better battleship for Canada, even a fictional upgrade? The game is called Naval War: Arctic Circle due for launch in the Spring 2013. Anyway here is the article I read but I want do dive into this more. Perhaps someday when Canada owns more than four rusty submarines.
A Norway based game developer has launched a new video game set in 2030 when NATO and Russian forces go head to head for Arctic Sovereignty. Doesn't sound that futuristic to me. Especially the best ship Canada has to offer is the HMCS Halifax class frigate built in the 80's. Seriously? They couldn't come up with a better battleship for Canada, even a fictional upgrade? The game is called Naval War: Arctic Circle due for launch in the Spring 2013. Anyway here is the article I read but I want do dive into this more. Perhaps someday when Canada owns more than four rusty submarines.
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